From: Hans Verkuil <hverkuil+cisco@kernel.org>
To: Pengpeng Hou <pengpeng@iscas.ac.cn>, Hans Verkuil <hverkuil@kernel.org>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>,
linux-media@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] media: cec: extron: validate response prefixes
Date: Wed, 9 Sep 2026 11:05:00 +0200 [thread overview]
Message-ID: <a589c1f2-e823-485f-9768-a6e471ffeaca@kernel.org> (raw)
In-Reply-To: <20260830130356.159-1-pengpeng@iscas.ac.cn>
Hi Pengpeng Hou,
On 30/08/2026 15:03, Pengpeng Hou wrote:
> extron_interrupt() dispatches completed serial lines by comparing fixed
> prefixes and reading fixed offsets without first checking the current line
> length. Short lines can therefore consume stale bytes beyond the
> NUL-terminated message item.
>
> Require each response type to contain the complete dispatch prefix before
> reading its fixed fields.
>
> Fixes: 056f2821b631 ("media: cec: extron-da-hd-4k-plus: add the Extron DA HD 4K Plus CEC driver")
> Signed-off-by: Pengpeng Hou <pengpeng@iscas.ac.cn>
> ---
> .../usb/extron-da-hd-4k-plus/extron-da-hd-4k-plus.c | 18 +++++++++---------
> 1 file changed, 9 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/media/cec/usb/extron-da-hd-4k-plus/extron-da-hd-4k-plus.c b/drivers/media/cec/usb/extron-da-hd-4k-plus/extron-da-hd-4k-plus.c
> index 3c6ce6f3d93e7..66780b3cf9188 100644
> --- a/drivers/media/cec/usb/extron-da-hd-4k-plus/extron-da-hd-4k-plus.c
> +++ b/drivers/media/cec/usb/extron-da-hd-4k-plus/extron-da-hd-4k-plus.c
> @@ -851,13 +851,13 @@ static irqreturn_t extron_interrupt(struct serio *serio, unsigned char data,
> if (debug)
> dev_info(extron->dev, "received %s\n", extron->data);
> extron->idx = 0;
> - if (!memcmp(extron->data, "Sig", 3) &&
> + if (extron->len >= 5 && !memcmp(extron->data, "Sig", 3) &&
All these extra checks makes the code fragile (i.e. easy to make mistakes), esp. if new
prefix checks are added in the future.
How about just replace:
extron->data[extron->len] = 0;
with:
/*
* Prevent the following prefix tests from using stale data
* from beyond extron->len
*/
memset(extron->data + extron->len, 0,
min(10, sizeof(extron->data) - extron->len));
This ensures that bytes extron->len to extron->len + 9 are all set to 0 and you won't hit
stale data.
Regards,
Hans
> extron->data[4] == '*') {
> extron_process_signal_change(extron, extron->data + 3);
> - } else if (!memcmp(extron->data, "Hdcp", 4) &&
> + } else if (extron->len >= 6 && !memcmp(extron->data, "Hdcp", 4) &&
> extron->data[5] == '*') {
> extron_process_edid_change(extron, extron->data + 4);
> - } else if (!memcmp(extron->data, "DcecI", 5) &&
> + } else if (extron->len >= 6 && !memcmp(extron->data, "DcecI", 5) &&
> extron->data[5] >= '1' &&
> extron->data[5] < '1' + extron->num_in_ports) {
> unsigned int p = extron->data[5] - '1';
> @@ -865,7 +865,7 @@ static irqreturn_t extron_interrupt(struct serio *serio, unsigned char data,
> p += extron->num_out_ports;
> extron_process_tx_done(extron->ports[p],
> extron->data[extron->len - 1]);
> - } else if (!memcmp(extron->data, "Ceci", 4) &&
> + } else if (extron->len >= 6 && !memcmp(extron->data, "Ceci", 4) &&
> extron->data[4] >= '1' &&
> extron->data[4] < '1' + extron->num_in_ports &&
> extron->data[5] == '*') {
> @@ -874,14 +874,14 @@ static irqreturn_t extron_interrupt(struct serio *serio, unsigned char data,
> p += extron->num_out_ports;
> extron_process_received(extron->ports[p],
> extron->data + 6);
> - } else if (!memcmp(extron->data, "DcecO", 5) &&
> + } else if (extron->len >= 6 && !memcmp(extron->data, "DcecO", 5) &&
> extron->data[5] >= '1' &&
> extron->data[5] < '1' + extron->num_out_ports) {
> unsigned int p = extron->data[5] - '1';
>
> extron_process_tx_done(extron->ports[p],
> extron->data[extron->len - 1]);
> - } else if (!memcmp(extron->data, "Ceco", 4) &&
> + } else if (extron->len >= 6 && !memcmp(extron->data, "Ceco", 4) &&
> extron->data[4] >= '1' &&
> extron->data[4] < '1' + extron->num_out_ports &&
> extron->data[5] == '*') {
> @@ -889,7 +889,7 @@ static irqreturn_t extron_interrupt(struct serio *serio, unsigned char data,
>
> extron_process_received(extron->ports[p],
> extron->data + 6);
> - } else if (!memcmp(extron->data, "Pceco", 5) &&
> + } else if (extron->len >= 7 && !memcmp(extron->data, "Pceco", 5) &&
> extron->data[5] >= '1' &&
> extron->data[5] < '1' + extron->num_out_ports) {
> unsigned int p = extron->data[5] - '1';
> @@ -899,7 +899,7 @@ static irqreturn_t extron_interrupt(struct serio *serio, unsigned char data,
> &tmp_pa[0], &tmp_pa[1]) == 2)
> extron_phys_addr_change(extron->ports[p],
> tmp_pa[0] << 8 | tmp_pa[1]);
> - } else if (!memcmp(extron->data, "Pceci", 5) &&
> + } else if (extron->len >= 7 && !memcmp(extron->data, "Pceci", 5) &&
> extron->data[5] >= '1' &&
> extron->data[5] < '1' + extron->num_in_ports) {
> unsigned int p = extron->data[5] - '1';
> @@ -910,7 +910,7 @@ static irqreturn_t extron_interrupt(struct serio *serio, unsigned char data,
> &tmp_pa[0], &tmp_pa[1]) == 2)
> extron_phys_addr_change(extron->ports[p],
> tmp_pa[0] << 8 | tmp_pa[1]);
> - } else if (!memcmp(extron->data, "EdidR", 5) &&
> + } else if (extron->len >= 7 && !memcmp(extron->data, "EdidR", 5) &&
> extron->data[5] >= '1' &&
> extron->data[5] < '1' + extron->num_ports &&
> extron->data[6] == '*') {
>
> base-commit: 08dbfad3f5040f5bdb6c529da20d6d4e81fefd72
prev parent reply other threads:[~2026-09-09 9:05 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-08-30 13:03 [PATCH] media: cec: extron: validate response prefixes Pengpeng Hou
2026-09-09 9:05 ` Hans Verkuil [this message]
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